1. Field of the Invention
The present invention relates generally to improvements in disc drive servo methods, and, more particularly, but not by way of limitation to improvements in noise reduction during track seeking in a disc drive.
2. Brief Description of the Prior Art
Disc drives are commonly used to provide long term storage of computer programs and files and, to this end, the programs and files are written to concentric data tracks defined on surfaces of rotating discs of the disc drive by transducers which "fly" above the surfaces in close proximity thereto. Subsequently, a program or file can be used by using the transducer to read the program or file for transfer into RAM of a computer with which a disc drive is used. Because of the large data storage capacity of a disc drive, computers having one or more disc drives provide an extremely versatile tool for a wide range of applications and, accordingly, such computers are in widespread use throughout business and industry.
A problem that has arisen with the introduction of computers, with their associated disc drives, into many business environments is that they can inject noise into those environments. The noise, generated by the disc drives, can be very distracting to those who work in such environments, especially in circumstances, increasingly common, in which a number of workers each use separate computers to carry out their assigned tasks.
An important first step in the reduction of noise generated by disc drives has been described in U.S. patent application Ser. No. 07/676,787 entitled "Method for Reducing Noise During Seeks in a Hard Disk Drive" filed Mar. 28, 1991 by Hampshire, McKenzie and Funches and incorporated herein by reference. As described in this United States Patent Application, noise can arise in the movement of the transducers from one data track to another, an operation generally referred to as a "seek" to a destination or target track. To accomplish such movement, the disc drive is comprised of a servo system that keeps track of the current location of the transducers with respect to the tracks on the disc surfaces and includes an electromechanical actuator, upon which the transducers are mounted, that receives control signals generated in part by a servo microcomputer to move the transducers radially across the disc surfaces. A control scheme commonly used is one in which the velocity of the transducers is repetitively compared to one of a plurality of a profile velocities stored in a look-up table that indicates, in relation to the distance between the transducers and the destination track, the velocity the transducers should have for movement to the destination track in accordance with a selected scheme for initially accelerating the transducers from an initial track and decelerating the transducers to the destination track.
A problem with this approach, discussed in the aforementioned U.S. patent application Ser. No. 676,787, now U.S. Pat. No. 5,475,545 is that generation of the control signal from a profile velocity, when the initial and destination track are widely spaced, will result in large acceleration of the actuator at the beginning of a seek and such acceleration has much the same effect as striking the actuator with a mallet. Specifically, to effect a large initial acceleration, the control signal transmitted to the actuator to cause the actuator to follow the velocity profile gives rise to large, rapidly increasing forces in initial portions of a seek that can excite vibration not only in the actuator but in the disc drive case which supports both the actuator and the discs. The result is excessive noise during the initial acceleration of the transducers away from the initial track from which the seek is commenced. As taught in this United States Patent Application, a large reduction in the noise associated with accelerating the transducers from the initial track can be achieved by accelerating the transducers in relation to the difference between the actual velocity of the transducers and a demand velocity that is derived from the stored profile velocities by selecting an initial demand velocity and thereafter incrementing the demand velocity in each of a sequence of time intervals during which the transducers are accelerated by a selected velocity demand fraction of the difference between each new profile velocity taken from the look-up table and the previous demand velocity. Such method will cause the actual velocity of the transducers to asymptotically approach the velocity profile while limiting the forces exerted on the actuator and the rate of change of such forces. Moreover, the method will have only a minimal effect on the time required to accomplish the seek, a consideration that is often of importance to the users of computers.
While the noise reduction method described in the aforementioned U.S. patent application Ser. No. 676,787 now U.S. Pat No. 5,475,545 was an important first step in the reduction of noise during seeks in a disc drive, it has been found that further noise reduction can be achieved during the acceleration the transducers from the initial track and, moreover, that noise arising from deceleration of the transducers can also be limited without significant effect on the operation of the disc drive or significant increase in the time required to effect a seek to a destination track.